The present invention relates to a liquid jetting head enabling to eject liquid in the state of droplet such as an ink jet recording head, a liquid crystal jetting head, a coloring material jetting head, etc., particularly to a head having a vibrator unit provided with a plurality of piezoelectric vibrators.
In the liquid jetting head enabling to eject droplet from a nozzle orifice by generating pressure fluctuation in liquid in a pressure chamber, there is an ink jet recording head discharging ink drops used for an image recording apparatus or the like. Recently, the head is applied for every kind of industrial equipment in view of an advantage that very little liquid can be ejected accurately. For example, the head is applied for a liquid jetting head enabling to eject liquid crystal, a coloring material jetting head enabling to eject coloring material for filter, an electrode material jetting head enabling to eject electrode material becoming an electrode, a bio-organic substance jetting head enabling to eject a bio-organic substance, a micro pipette (a sample jetting head) enabling to eject a very little sample accurately, and so on.
In the various kinds of types of such the liquid jetting head, there is a type wherein liquid droplets are ejected by expanding or contracting piezoelectric vibrator. For example, 30-200 pieces of piezoelectric vibrators are arranged for each nozzle row. In a practical use, a plurality of piezoelectric vibrators are integrated as a unit to improve assembling efficiency. This vibrator unit comprises a vibrator assembly in which a plurality of piezoelectric vibrators are formed in a pectinated manner, a fixing plate on which the vibrator assembly is bonded, and a wiring board for supplying power to the respective piezoelectric vibrators. As the piezoelectric vibrator, there is preferably adopted a laminated type vibrator in which common electrodes and drive electrodes are alternately laminated while sandwiching a piezoelectric material. The laminated type vibrator extends or contracts in accordance with a potential difference between the drive electrode and the common electrode. In this respect, the common electrodes are grounded while the potential of the drive electrode in each of the vibrators is controlled by applying a drive signal. The fixing plate is a plate member for receiving the kinetic energy of the vibrators. Metal plate such as stainless steel is preferably adopted in view of the stiffness and the heat radiating property.
The common electrodes and the wiring board are electrically connected via an external common electrode formed on an outer face of the vibrator assembly. When the vibrator assembly is bonded on the fixing plate, the external common electrode and the fixing plate may be directly contacted with each other at a portion where an adhesive is not interposed therebetween. In such a case, the potential of the fixing plate becomes the same as that of the common electrodes.
As the wiring board, a flexible sheet type one is preferably adopted. To efficiently use limited spaces, a controller IC for controlling the driving of the piezoelectric vibrators is provided on a surface of the wiring board. To facilitate insertion operation of the wiring board into a head case, and to enhance the heat radiation property, the controller IC is bonded onto the fixing plate as disclosed in PCT International Publication No. WO98/57809.
To make the liquid jetting head compact, the thinner controller IC is preferable. Specifically, it is preferable that the thickness of the controller IC is thinner than the thickness of the vibrator assembly. To reduce the thickness of the controller IC, a face opposite to a face of the controller IC mounted on the wiring board is abraded. That is, only the mounted section is molded and an oxide film in the abraded side is removed. The abraded face is bonded to the fixing plate.
In this case, there is a possibility that the abraded face and the fixing plate are conducted with each other. For example, in a case where the controller IC is pressed against the fixing plate in a condition that the adhesive is not solidified, the abraded face and the fixing plate may directly contact with each other while pushing aside the unsolidified adhesive. Accordingly, there is possibility that the common electrodes of the vibrators and the fixing plate are conducted with each other through the abraded face of the controller IC.
However, since the common electrodes are grounded, there is no considerable problem even if the common electrodes and the abraded face of the controller IC through the fixing plate.
Incidentally, insulating resistance of the piezoelectric material possibly falls by long use of the piezoelectric vibrator. When the insulation fault generates, the drive electrodes and the common electrodes in the vibrators are happened to be conducted with each other, so that the potential of the drive electrode falls down to the ground potential. In this state, when high potential driving signal is supplied to eject liquid drop, the volume and the speed of expansion and contraction of the piezoelectric vibrator become large inordinately, so that liquid drop is ejected unexpectedly.
In order to prevent such an accidental ejection, it is considered that constant bias potential which is higher several V to ten and several V than the ground potential and lower than intermediate potential is applied to the common electrode. In this case, since the potential of the drive electrode falls to at (east the bias potential even if insulation fault generates, the accidental liquid drop ejection can be prevented.
However, in a case where the common electrodes and the abraded face of the controller IC are conducted through the fixing plate under a condition that the bias potential is applied to the common electrodes, the bias potential is applied to the abraded face of the controller IC. Accordingly, fault and malfunction of the controller IC may be caused.
It is therefore an object of the present invention to provide a structure of liquid jetting head in which insulation of the fixing plate and the controller IC can be surely attained, and manufacturing efficiency is improved.
In order to achieve the above object, according to the present invention, there is provided a liquid jetting head, comprising:
a fixing plate, including a first region and a second region;
a vibrator assembly, including a plurality of piezoelectric vibrators, a drive electrode formed on each of the piezoelectric vibrators, and a common electrode formed commonly to the piezoelectric vibrators, the vibrator assembly bonded onto the first region in a cantilevered manner;
a sheet-shaped wiring board, which supplies a drive signal to the drive electrode and applies a bias potential which is higher than a ground potential to the common electrode;
a controller IC, which controls the drive signal, the controller IC having a first face mounted on the wiring board, and a second face opposing to the first face in which a semiconductor surface is exposed; and
an insulating layer, interposed between the second region of the fixing plate and the second face of the controller IC.
In this configuration, the controller IC can be surely prevented from charging the bias potential even if the common electrode contacts the fixing plate. Therefore, fault and malfunction of the controller IC can be surely avoided.
Preferably, the insulating layer is a resin film formed on the second region of the fixing plate. In this case, an extremely thin insulating layer can be easily formed.
Here, it is preferable that the resin film is formed by an adhesive used for bonding the vibrator assembly and the fixing plate. In this case, the resin film can be formed when the vibrator assembly is bonded on the fixing plate.
To easily obtain the insulating layer, the insulating layer may be a resin sheet adhered on the second face of the controller IC.
According to the present invention, there is provided a manufacturing method of a liquid jetting head, comprising:
providing a fixing plate, including a first region and a second region;
providing a vibrator assembly including a plurality of piezoelectric vibrators;
providing a sheet-shaped wiring board on which a first face of a controller IC is mounted;
exposing a semiconductor surface at a second face of the controller IC opposing to the first face;
coating an insulating adhesive on the first region of the fixing plate;
coating an insulating adhesive at least one of the second region of the fixing plate and at least a part of the second face of the controller IC;
placing the vibrator assembly onto the first region;
placing the second face of the controller IC onto the adhesive on the second region of the fixing plate; and
solidifying the adhesive on the first region and the adhesion on at least one of the second region and the second face to bond the vibrator assembly and the controller IC onto the fixing plate.
In this method, the manufacturing can be efficiently performed because the insulating layer can be formed between the controller IC and the fixing plate while the vibrator assembly is bonded onto the fixing plate.
When the adhesive is coated on a part of the second face of the controller IC, the adhesive can be selectively applied on a desired portion so that the coating amount of the adhesive may be managed roughly to improve the manufacturing efficiency. Especially when a photocuring adhesive is adopted, such an adhesive may be selectively coated on a portion to which light such as ultraviolet light is irradiated so that the coated adhesive can be surely cured without remaining uncured portions.
Preferably, the semiconductor surface is exposed by abrading the second face of the controller IC.
According to the present invention, there is also provided a manufacturing method of a liquid jetting head, comprising:
providing a fixing plate, including a first region and a second region;
providing a vibrator assembly including a plurality of piezoelectric vibrators;
providing a sheet-shaped wiring board on which a first face of a controller IC is mounted;
exposing a semiconductor surface at a second face of the controller IC opposing to the first face;
coating an insulating adhesive on the first region and the second region of the fixing plate;
placing the vibrator assembly onto the first region;
solidifying the adhesive on the first region and the adhesion on the second region;
coating an adhesive at least one of the vibrator unit and the flexible cable;
placing the wiring board onto the vibrator unit while placing the second face of the controller IC onto the solidified adhesive on the second region of the fixing plate; and
solidifying the adhesive interposed between the vibrator unit and the flexible cable.